AND CORRESPONDING METHOD

The present invention relates to laminating apparatus for laminating multilayer articles, in particular photovoltaic modules. The invention also relates to processes for lamination of multilayer articles.

In a number of areas of technology, multilayer articles are laminated together. The layers of the article may interact in order to provide properties such as strength, toughness or transparency. Alternatively, the article may have layers of protective material and active layers within it.

US-2008/0295956-A1 relates to a method and a device for laminating plate-shaped workpieces with at least one adhesive layer that can be heat activated and cured under the effect of pressure and heat. A number of workpieces is inserted into a multiple-stage vacuum lamination press In which the workpieces are laminated in press stages with a vacuum chamber divided by flexible pressure member. Each laminating plate has a conveyor belt around it for feeding and delivering the work pieces by transferring them through the multiple-stage laminator. The work pieces are transferred between the various lamination stages (zones) by using such conveyor belts.

US-2008/0295967-A1 relates to a multi-layer laminating press for laminating planar work pieces under the influence of pressure and heat. Also in this case the work pieces are transferred between the various lamination stages (zones) by using such conveyor belts.

US-2009/0242137-A1 relates to a stacked laminator comprising multiple vertically stacked laminating units and provides a more compact laminator and improves the efficiency with which workpieces are produced. Each laminating unit comprises an upper and a lower plate so that the laminator is practically a multiple assembly of standard laminators (single unit) stacked up together.

One important type of multilayer article is a photovoltaic (PV) module. In order to provide useful power for various applications, individual solar cells must be connected together to give the appropriate current and voltage levels and they must also be protected from damage by the environment in which they operate. This electrically connected, environmentally protected unit is usually called a photovoltaic module or a PV laminate. The module may be used alone or connected in an electrical circuit with other similar modules to form a photovoltaic array. Module designs tend to follow the same basic principles but may differ in a number of respects depending upon the particular type of PV cell incorporated within the module.

Generally, the front surface of a PV module is composed of a glass sheet. The back surface layer of the module may be made from a number of materials. For example, the back surface may be a plastic sheet or may be a second sheet of glass. The glass-glass structure is particularly popular for incorporation into glazed facades or roofs.

In the production of a PV module, the electrically connected PV cells are sandwiched between other layers of the multilayer lamination. For example, in crystalline silicon PV modules, the electrically connected PV cells are sandwiched between two sheets of encapsulant plastic (a common type of encapsulant is ethylene vinyl acetate, EVA or polyvinyl butyral, PVB) the front glass sheet and rear plastic sheet are then added and the whole structure is laminated in a laminating apparatus. The lamination involves placing the PV module in a holding chamber, application of vacuum to the multilayer article from the inside of the chamber, application of pressure from the outside to the module and heating of the module in order to soften, melt or cure the encapsulant improving the quality of the seal.

In other types of PV module, for example, a thin film module, a single layer of encapsulant is often used. The thin film PV cells are often coated on the (inside) surface of the front glass sheet and a layer of encapsulant is used in order to join the coated glass sheet, containing the thin film PV cells, to a backing sheet of plastics or glass.

US-A-5, 593,532 relates to a process for making photovoltaic modules and devices to implement same. US-B-6,481 ,482 relates to a similar process and laminating apparatus for manufacturing a photovoltaic module. US-B- 6,481 ,482 addresses the problem of warping by asymmetrical heating of the top and bottom surfaces of the PV module. This patent overcomes this problem by providing a holding chamber where the multilayer article is contained with heating in both the upper and lower surfaces.

In both of these documents, the PV module to be laminated is held in a two component laminating chamber having a bottom plate and a top plate each with independent heaters. Each laminating chamber can provide to the multilayer article heating, vacuum or pressure. Unfortunately, such an arrangement leads to complexity and is not an efficient use of space or energy, especially in view of the modern need for increased productivity in a PV module manufacturing facility. Furthermore, the rate of production of the manufacturing facility depends upon the number of laminating chambers which have been installed in the facility. It is difficult, In practice, to add more chambers in the known devices in order to increase productivity.

It is, of course, important to ensure relatively even heating of the top and bottom surfaces of PV modules in the lamination apparatus, both to reduce or prevent warping, and also to ensure that thermal shock and/or stresses induced by different rates of heating are minimised. This is especially true because many PV modules use one or more glass sheets in their construction.

It is an aim of the present invention to provide multichamber laminating apparatus and processes for laminating multilayer articles which avoid or mitigate the problems associated with the prior art and save space and energy.

The present invention accordingly provides laminating apparatus for laminating two or more multilayer articles, the apparatus comprising a pallet with three or more laminating plates, at least two of the laminating plates being adapted for holding a multilayer article for lamination, wherein the laminating plates and/or pallet are adapted so that the multilayer articles undergo the complete lamination process while on their respective laminating plates, wherein each laminating plate comprises a heating means and wherein the laminating plates are overlapped (i.e. in a stacked configuration) so that each multilayer article is capable of being heated on the bottom surface thereof by the heating means of the laminating plate by which it is P T/EP2010/062917

held and on its top surface by the heating means of the neighbouring plate above.

Preferably each multilayer article is contained in a holding chamber between two separate laminating plates which can provide heating, vacuum and/or pressure.

The three or more overlapped laminating plates forming two or more laminating holding chambers together with its holding means is herein referred to as a pallet which is loaded with the multilayered articles at the beginning of the laminating cycle and unloaded at its end.

The great advantage of a laminating apparatus according to the first aspect of the invention is that, because each of the laminating plates may function both as the holding and the bottom heating means for the multilayer articles to be laminated as well as the heating means for the top surface of the neighbouring multilayer article below, apparatus according to this invention is much more compact and so more efficient in terms of usage of space and energy. Furthermore, the system is more flexible in the sense that the number of laminating plates (holding chambers) may be tailored easily in the apparatus to the specific needs increasing flexibility and in particular enabling an increase or reduction to the production capacity of a particular lamination installation in the design phase.

Furthermore, because the design of the apparatus is based on a pallet with multiple laminating plates the multilayer articles remain on their respective laminating plates throughout the laminating process thereby removing the need for conveying devices to convey the individual articles. This means that each multilayer article is substantially stationary on its laminating plate in the pallet during lamination.

In some embodiments of the invention, the pallets may move (e.g. in a carousel-type system) or be stationary but in all embodiments of the invention the modules/articles are stationary in the pallet or pallets during the lamination process.

Preferably, the apparatus comprises one or more laminating pallets each pallet comprising (i.e. for receiving) three or more laminating plates. Another advantage is that, since ail the laminating plates (except optionally for the top and the bottom ones) at the same time have equal pressure and/or preferably vacuum on both sides, they can be made relatively thin because no differential pressure exists between them so saving material and decreasing their thermal inertia.

Each laminating pallet may contain from 3 to 14 laminating plates or more. Typically, a number of the laminating plates (except, preferably, for the top and bottom ones), will be substantially similar or identical, each capable of holding one or more multilayer articles and heating those articles on the bottom surface and providing heating means for the top surface of the articles which is held by the neighbouring laminating plate below.

Preferably, the pallet will further comprise a top laminating plate which is of slightly different construction in that it does not (necessarily) have any components for holding multilayer articles but instead contains heating means for heating the upper surface of multilayer articles on the plate below and has to withstand the differential pressure with the ambient.

Preferably, the pallet will comprise a bottom laminating plate which is adapted to hold one or more multilayer articles, has to withstand the differential pressure with the ambient but is not necessarily provided with heating means to heat other multilayer articles, below.

Generally, the pallet will be arranged so that the laminating plates are placed above one another from a top laminating plate to a bottom laminating plate.

Generally, the multilayer article will comprise at least one glass layer. Preferably each multilayer article is a photovoltaic module. The photovoltaic module may contain amorphous silicon, crystalline silicon, thin film or any other type of photovoltaic cell. Generally each multilayer article will contain a top substrate, at least one layer of encapsulant, an active layer containing one or more photovoltaic cells (which may, for example, in the case of thin film photovoltaic cells be coated on the inner side of the top substrate, typically a glass sheet) and a bottom sheet which may be of plastics or glass. Further layers of encapsulant and other active or protective layers may be incorporated within a PV module laminate made with crystalline cells.

Apparatus according to the invention will preferably further comprise at least one lamination station in which one or more pallets each made of three or more laminating plates may perform the whole lamination process.

Typically, there may be a number of laminating stations in the apparatus preferably in zones where the pallets will go through during the lamination process. In different zones, different steps of the lamination process will generally take place. For example in the first zone, a vacuum step may take place where the multilayer article is deaerated. Then, it is heated at a relatively slow rate. In this or other zones/stations heat, vacuum and/or pressure steps may take place where heat, vacuum and/or pressure is applied to the multilayer article in order to ensure efficient lamination.

The, or each, lamination station is usually adapted to receive one or more laminating pallets. If there is more than one laminating station, then preferably there is also means provided to transfer the, or each, laminating pallet between each laminating station. The means to transfer the or each pallet between each station/zone may comprise conveying means. Thus, the apparatus may further comprise conveying means adapted to transport at least one pallet through the different phases of the lamination cycle.

Preferably, the, or each, laminating pallet may be loaded (and optionally unloaded) with robot means. This embodiment is particularly advantageous because it requires relatively low capital costs and has a much reduced footprint. If the apparatus is such that loading/unloading is to be done by robot means then the laminating pallet may preferably be adapted to hold a larger number of laminating plates e.g. 3 to 14, preferably 6 to 12, more preferably 7 to 11.

If the apparatus is intended to not be conveyed between stations/zones, it is, nevertheless, advantageous if the apparatus has conveying means to allow the apparatus (especially the pallet) to be moved to a repair/maintenance area. In a preferred embodiment of the present invention, the apparatus further contains lifting means for changing the distance between the multilayer article and the laminating plate on which it is lying. The benefit of this feature is that the lifting means, by adjusting the distance between the multilayer article and its laminating plate also changes the distance between the multilayer article and the heating means within the laminating plate. Consequently, the rate of heating may be changed by using the lifting means to reduce or minimise thermal shock and also to ensure flexibility of heating and cooling rates of the multilayer article. These lifting means allow also a better deaeration of the space between the multilayer article and the laminating plate it is laying on.

Preferably, the lifting means comprises three or more lifting pins. The lifting pins may, for example, be situated below or within the laminating plate holding the multilayer article and the laminating plate and lifting pins may be adapted so that the lifting pins pass through the laminating plate and raise the multilayer article above the laminating plate.

Preferably the lifting pin may be moved by mechanical bars due to inclined level and/or variable thickness of the bars. Preferably (especially if loading/unloading by robots) the lifting means are adapted to raise the articles by 7mm or more preferably 9mm or more above the laminating plates.

The heating means of the apparatus, and in particular the laminating plates, preferably comprises flexible heating means (e.g. flexible silicone heaters).

The laminating plate also preferably comprises pressure means for applying pressure to the multilayer article in the bottom neighbouring plate and/or vacuum means. The pressure means may comprise a flexible membrane and may also comprise a membrane chamber and which is preferably a vacuum and/or pressure chamber. Gas may be introduced into the pressure chamber so as to flex the flexible membrane towards the multilayer article on the bottom neighbouring plate thereby enabling pressure to be applied to the multilayer article on the bottom neighbouring plate. If the membrane chamber is also capable of being evacuated to a slightly lower pressure than that existing in the holding chamber, then that provides a convenient means for moving the flexible membrane away from the multilayer article on the bottom neighbouring plate at the appropriate point in the lamination cycle.

The or each laminating plate may also comprise cooling means, preferably means for circulating a cooling fluid (e.g. chilled air), to cool down the multilayer article. Cooling means may also be associated with parts of the apparatus other than the plates.

Generally, each laminating plate will comprise a heat conductive base. A preferred type of heat conductive base is a metallic body, preferably comprising aluminium. Generally, it is preferred if the heat conductive base is of substantial thermal conductance for ensuring an even temperature on the surface of the multilayer article.

In a second aspect of the present invention, there is provided lamination apparatus for laminating two or more multilayer articles, the apparatus comprising at least two laminating plates for holding multilayer articles for lamination, and lifting means for changing the distance between the multilayer articles and the laminating plate.

The present invention provides, in a third aspect, laminating plates for laminating multilayer articles, each laminating plate comprising a heat conductive base, a holding chamber for receiving the multilayer article, the holding chamber being positioned on the upper side of the plate, a flexible membrane on the lower side of the plate (except optionally for the bottom laminating plate), a membrane chamber (except optionally for the bottom laminating plate) situated between the lower side of the plate and the membrane, and heating means for heating the multilayer articles.

Thus, preferably the laminating apparatus comprises a laminating plate according to the third aspect of the invention. Preferably, the laminating plate is such that the flexible membrane is held by a frame to which is attached and the frame can slide in two guides, placed at two opposite sides of the frame, to allow for a rapid membrane replacement.

The present invention provides, in a fourth aspect, a process for lamination of two or more multilayer articles, the process comprising, providing a pallet comprising three or more laminating plates each having a heating means, at least two plates being adapted to hold multilayer articles for lamination, arranging the laminating plates in a stacked configuration in the pallet so that each multilayer article is capable of being heated on the bottom surface by the heating means of the laminating plate in which it is held and on the top surface by heating means of the neighbouring plate above, heating the multilayer articles, whereby the multilayer articles undergo the complete lamination process while on their respective laminating plates.

The present invention provides in a fifth aspect a process for lamination of at least two multilayer articles, the process comprising, deaering, pre-heating, for a pre-determined time, at least one surface of the multilayer article by convection and/or radiation, and subsequently heating the surface by conduction.

Embodiments of the invention will now be described with reference to the following drawings in which:

Figure 1 illustrates a perspective view of a laminating pallet according to the present invention.

Figure 2 illustrates a front view of a laminating pallet

Figure 3 illustrates a front cross sectional view of a laminating pallet in open position taken through the line A-A of Figure 2.

Figure 4 illustrates a front cross sectional view of portions of laminating plates containing multilayer articles including in (a) a top laminating plate, (b) intermediate laminating plates, and (c) a bottom laminating plate.

Figure 5 illustrates a pin lifting device for changing the distance between the multilayer articles and the laminating plate.

Figure 6, illustrates a plan view of lamination apparatus according to the present invention comprising a number of zones .

Figure 7 illustrates lamination apparatus according to the present invention where the laminating pallet is essentially stationary during lamination.

The apparatus as illustrated in the Figures is capable of the lamination of the "sandwich" that constitutes the PV module, mono-crystalline, poly crystalline or based on thin film that has previously been pre-assembled on the upstream lines in an automatic or manual way with e.g. glass sheets and encapsulant (e.g. EVA or PVB).

Typically, PV modules having the following dimensions may be laminated: Minimum 500 mm x 1000mm

Maximum 1200mm x 2000mm

Total thickness of the module:

Minimum 5 mm.

Maximum 20 mm.

Figures 1 , 2 and 3 illustrate a laminating pallet, which is the main process component of the lamination system. The pallet 1 is essentially constituted by a steel supporting frame that contains 6 lamination plates 2, 3, 4, 5, 6, 7 made in aluminium, plate 7 being the top plate, and the system to sustain and guide the vertical movement of these plates. Plate 2 is the bottom plate.

Figure 4 illustrates a front cross sectional view of portions of the laminating plates 2, 3, 4, 7. Figure 4(b) illustrates intermediate laminating plates 3, 4 each comprising a lower (membrane) chamber 9 with membrane 1 1 to apply pressure or vacuum to the bottom neighbouring module, a holding chamber 8 containing the module to be laminated, a heating means 10 with electrical compact heaters (silicon rubber flexible heaters) attached below the laminating plates. The membrane 11 is held by the frame 52 to which is attached with the rim 53 and the frame carrying the membrane can slide in the guides 54, placed on two opposite sides of the frame, to allow for a rapid membrane replacement. The gaskets 55 and 56 prevent leakage of the holding and of the membrane chambers during the lamination process. Figure 4(a) illustrates the top laminating plate which has not the holding chamber. Figure 4(c) illustrates the bottom laminating plate which has not the membrane chamber, the membrane and the membrane frame and rim.

Figure 5 illustrates a pin/peg-table system with a cursor 102, and pins 100 which may be embedded into the heating plate. Controlled upward movement of the pins 100 can be used to lift the modules from the heating table. Figure 6 illustrates a laminating apparatus in which one or more pallets move through various stations during the lamination process.

The parts of Figure 6 are as follows:

12 Multi-level transfer

13 Entry conveyor

14 Vertical accumulator with 5 levels

15 Closing plates station with peg-table device, plates clamping device and glass loading system

16 Lamination tunnel

17 Conveyor system. Production process and handling circuits

18 Opening plates station with pin/peg table device, plates unlocking device and glass unloading system

19 Vertical accumulator with 5 levels

20 Exit conveyor

21 Mult, level transfer

22 Systems to apply vacuum, pressure and electricity

The lamination apparatus illustrated in Figure 6 works in the following way.

The first multilayer article, pre-assembled on the upstream preparation line, enters into the entry conveyor 13 and then is conveyed into the vertical accumulator 14.

The accumulator moves up by one step.

The cycle is repeated four more times until the accumulator is full with modules with equal distance between them.

At the same time one multilevel laminating pallet enters into the station

15.

The multilevel transfer system 2 takes from the accumulator the modules that were previously loaded in it and loads them simultaneously into the pallet positioned into the station 15.

As soon as the pallet has been loaded, in the same station 15 a special device closes the six plates and blocks them together.

Each pallet contains five lamination plates. At this point the pallet is ready to be processed into the lamination tunnel 16 that can at the same time receive 8 pallets to be processed.

The lamination process is performed in a manner that is explained below.

The laminating process may comprise various steps taking place in the laminating chambers 71 to 78 in the zones 41 , 42, 43, 44 illustrated in Figure 6.

During lamination, vacuum down to 1 mbar may be applied, a temperature (closely controlled) of up to 80°C and a maximum pressure of up to 2000 mbar may be applied to the multilayer article. The conditions of lamination and individual lamination steps depend upon the multilayer article to be laminated.

When the pallet exits from the lamination tunnel if necessary the multilayer articles may be subject to a process of natural or forced cooling to obtain the right temperature at which they can be automatically unloaded from the pallet.

Following the cooling station the pallet enters into the station 18 where a dedicated system releases and opens the lamination plates that are inside the pallet.

In this way the pallet is ready to be unloaded from the five modules contained in it and after being unloaded to return to station 15.

The unloading operation is handled through the multilevel transfer 21 that has the task of unloading the pallet, loading the vertical accumulator 11 and then feed continuously the exit conveyor that will send the module to the finishing line.

The lamination tunnel is mainly constituted by a supporting steel frame 10 that is extremely well insulated to avoid heat losses.

Within this tunnel there is a conveying system 17 to move the pallets 1.

The tunnel is able to contain 8 pallets in process.

In parallel to the main axis of the tunnel the services supply systems 22 are to supply vacuum, pressure and electricity to the pallets. This services supply system 22 is able to supply automatically electrical energy, compressed air and vacuum that are required for the lamination process.

In the zones 41 to 44 there are automatic connection carriages capable of x-y movement that, after having been connected automatically to the pallets, follow them remaining connected to the pallets while they are travelling through the zones 41 to 44.

Each pallet as illustrated in Figures 1 , 2 and 3 moves along the tunnel allowing the possibility of conveying through the lamination tunnel (of e.g. Figure 6) five PV modules per each pallet at the same time. Of course, more or fewer modules may be laminated simply by changing the number of laminating plates in each pallet, and/or by loading two or more multi-layer articles in each holding chamber 8.

The lamination occurs with the functional interaction between the pallets, conveying system and automatic systems to apply, pressure, vacuum and electrical heating that are present along the tunnel.

Assuming a total process time of 16 minutes per pallet, the entire system represented in Figure 6 will be able to process 150 modules/hour.

Figure 7 illustrates an alternative embodiment of the apparatus where the pallet 1 is essentially stationary during the lamination process. The pallet is loaded by a robot 200 with multilayer articles for lamination and unloaded by a robot 202.

The apparatus comprises an entry conveyor 204, a loading robot 200, the pallet 1 , the unloading robot 202 and the exit conveyor 206. Depending on the size of the laminating plates, it may be possible to load either one or more multilayer articles on each plate. Typically a lamination pallet according to this embodiment would have greater capacity, usually able to hold 10 laminating plates although fewer or more lamination plates may be used if desired.

Alternatively, the same robot can both load and unload the pallet.

An advantageous component of the apparatus illustrated in Figure 7 is a maintenance system comprising rails 210 to allow the pallet to be moved out of the operating area to a position 208 where the pallet and/or laminating plates can be maintained and/or repaired, in particular, to allow replacement of the membranes which have a limited life in use.